Woodpecker is a very popular email marketing tool for sending cold emails with follow-ups.
It can be used for many things, including link building when doing outreach for SEO.
They do not pay as high commissions as other email marketing tools. But their product is not the same as those other affiliate programs as they do not do email list building and newsletter tools.
They pay a flat 20% recurring revenue share. I believe the commission is recurring for the lifetime of your referrals.
Woodpecker costs from $40/mo per seat. That means you can earn from $8/mo for each client you send their way.
They offer a 30-day free trial.